Water runs through it

Reduce runoff with hardscape options that redirect rainwater into the ground

By Mary James • Special to the U-T
| 4:25 p.m.Oct. 28, 2011

A new fountain at the Water Conservation Garden at Cuyamaca College is surrounded by permeable concrete, which allows rainwater or irrigation to soak through to the soil. The garden showcases water-wise hardscaping options.
— Nelvin C. Cepeda

A new fountain at the Water Conservation Garden at Cuyamaca College is surrounded by permeable concrete, which allows rainwater or irrigation to soak through to the soil. The garden showcases water-wise hardscaping options.
— Nelvin C. Cepeda

Decomposed granite (DG): Finely ground rock compacted or hardened to create a firm surface is ideal for level paths, flat driveways, patios and parking areas. Available in many colors for natural or decorative landscaping. Used for all the paths at the Water Conservation Garden.
Cost: Relatively inexpensive; about one-fourth the cost of concrete.

+Read Caption

Decomposed granite (DG): Finely ground rock compacted or hardened to create a firm surface is ideal for level paths, flat driveways, patios and parking areas. Available in many colors for natural or decorative landscaping. Used for all the paths at the Water Conservation Garden.
Cost: Relatively inexpensive; about one-fourth the cost of concrete.

Bricks or pavers of stone or concrete set on sand: “Tried and true,” says Sherman of this ancient technique. Bricks or pavers are packed tightly together on a bed of sand, minus any concrete, so water seeps through. Requires a level base equal to the depth of the bricks. Over time, roots or soil movement may displace bricks that will have to be pulled out and reinstalled. Good for paths, patios or light-traffic driveways. See an example outside the amphitheater at the Water Conservation Garden.

+Read Caption

Bricks or pavers of stone or concrete set on sand: “Tried and true,” says Sherman of this ancient technique. Bricks or pavers are packed tightly together on a bed of sand, minus any concrete, so water seeps through. Requires a level base equal to the depth of the bricks. Over time, roots or soil movement may displace bricks that will have to be pulled out and reinstalled. Good for paths, patios or light-traffic driveways. See an example outside the amphitheater at the Water Conservation Garden.

Decomposed granite (DG): Finely ground rock compacted or hardened to create a firm surface is ideal for level paths, flat driveways, patios and parking areas. Available in many colors for natural or decorative landscaping. Used for all the paths at the Water Conservation Garden.

Cost: Relatively inexpensive; about one-fourth the cost of concrete.

Bricks or pavers of stone or concrete set on sand: “Tried and true,” says Sherman of this ancient technique. Bricks or pavers are packed tightly together on a bed of sand, minus any concrete, so water seeps through. Requires a level base equal to the depth of the bricks. Over time, roots or soil movement may displace bricks that will have to be pulled out and reinstalled. Good for paths, patios or light-traffic driveways. See an example outside the amphitheater at the Water Conservation Garden.

Cost: Equivalent to concrete.

The newest exhibit at the Water Conservation Garden looks like a typical burbling fountain until Executive Director Marty Eberhardt throws some water on the concrete that encircles it. In an instant, the water vanishes.

This disappearing act owes its magic to permeable concrete that allows water to pass through to the ground below. It is one of several eco-friendly hardscape options showcased at the 5-acre demonstration garden on the campus of Cuyamaca College in El Cajon. Admission is free, and the garden is open daily from 9 a.m. to 4 p.m.

Since 1999, the garden has been in the forefront of water conservation education, whether helping homeowners lose their thirsty lawns, turning HOAs on to water-smart landscaping or inspiring kids with the educational antics of “Miss Smarty Plants.”

This new exhibit marks a broadening of its mission, Eberhardt says. “We want to be a model for sustainable green living beyond water conservation,” she explains. “This exhibit is about stormwater management and how important it is not to pollute our waterways with toxic urban runoff.”

A few years ago, the garden augmented its many water-saving displays — everything from drought-tolerant gardens to irrigation how-tos — with a rainwater collection exhibit. It demonstrates one way to make the most of the region’s sparse annual rainfall and reduce pollution by diverting roof runoff into a storage tank where the water can later be used for irrigation.

But, arguably, even more runoff streams off patios, driveways, sidewalks, paths and other paving, carrying debris and pollutants into storm drains and ultimately the ocean. That awareness has sparked renewed interest in permeable hardscaping, ranging from permeable concrete to decomposed granite and gravel.

“The goal is to get as much rainwater as possible into the soil, where it benefits gardens and recharges natural aquifers,” says Cardiff landscape architect Steve Sherman of California Landscape Technologies. “Permeable paving is often an inexpensive way to achieve it.”

Nov. 5 at the garden’s annual Fall Home and Garden Festival, Sherman will discuss permeable surfaces at a free class, one of several planned at the all-day event. Details are at

The garden’s newest exhibit, funded by the county’s Watershed Protection Program, showcases concrete that’s less dense than standard concrete, a mix of aggregates and cement. The use of larger aggregates minus small gap-filling “fines” creates a permeable surface that water passes through.

Not as tough as concrete, permeable concrete is best for walks, patios and light-traffic roads, Sherman says. (Driveways can be problematic, depending on their slope and the weight of vehicles parked there.) Aesthetically, permeable concrete resembles hand-seeded concrete where the aggregate is exposed, rather than hidden under smooth cement. “It’s a custom look, but not one everybody likes,” Sherman says.

Compared with standard concrete, permeable concrete costs about 15 percent to 20 percent more, Sherman notes. In new construction, that increase often is offset by reduced need for other more expensive drainage solutions. For this and all other permeable pavement options, Sherman emphasizes the need for proper site selection and preparation. Pouring and finishing concrete is not a DIY project — consult with a landscape architect or designer and have the installation done by an experienced licensed contractor.

Below are some other permeable paving options. “All of these can be used creatively in a million different ways and combinations to be environmentally friendly,” Sherman says.

Gravel: Used for centuries, washed and cleaned crushed rock is a highly permeable ground cover as well as surface for patios, paths, driveways and access roads. Avoid rounded pebbles because “you sink when you walk on them,” Sherman says. “But if you like to walk barefoot, sharp-edged gravel isn’t for you.” This stone is available in “every color, shape and size imaginable,” he adds. Cost: One of the least expensive options.

Permeable pavers: These pavers of stone or concrete have clipped corners or cutouts that are filled with sand to allow water to seep into the ground. Set on a bed of sand with no concrete seams. Available in a variety of designs and colors. Useful for driveways, parking areas, paths or patios.

Cost: Equivalent to concrete.

“All paving requires an adequately prepared base and may benefit from a filter fabric layer below,” Sherman notes. “And both DG and gravels should be installed 2 to 6 inches, deep depending on the intended use.”